1. Field of the Invention
The present invention broadly relates to a non invasive method for the detection of a mechanical abnormality or injury of the lumbar spine of a patient
The invention more particularly relates to a non invasive method and equipment for the detection of torsional injuries in the lumbar spine of a patient.
2. Brief Description of the State of the Art
It is well known in the medical art that common back disorders have a mechanical etiology. Pathology clearly shows that there are two common patterns of disk injuries which correspond to two different types of mechanical failure of the spine.
The first injury which is generally identified as "compression injury", starts centrally with a fracture to an end plate of a lumbar vertebra, sometimes followed by injection of part of the vertebra nucleus into the vertebral body. In this particular case of injury, neither the annulus of the disk nor the facets of the vertebra are damaged However, the injured end plate permits the invasion of the avascular nucleus and the avascular inner portion of the annulus by granulation (healing) tissue. The effect of this is to dissolve or hydrolyze the avascular portion of the disk. With progression, the disk losses its thickness while the outer layers of the annulus remain relatively well preserved. With loss of disk thickness, the facet joints of the vertebra subluxates and becomes arthritic.
In practice, the fracture on the end plate of a vertebra is an undisplaced fracture of cancelleous bone which heals rapidly. The symptoms are short lived, typically lasting two weeks. The facet joint arthritis appears late. At this stage, symptoms may also arise from a reduction in size of the spinal canal (lateral or central spinal stenosis).
The second common back disorder which is generally identified as "torsional injury", amounts to a damage of the disk annulus, which damage occurs simultaneously with a damage to the facet joints of the vertebra. The outer rings of the annulus are torn off the vertebral end plate, and separation occurs between the laminations of the annulus. There is no damage to the nucleus or to the end plate of the vertebra. The facet joints show subchondral fracture, with consequence collapse of the articular surfaces and chronic synovitis.
In this particular case, the basic injury is to collageneous ligamentous tissue which requires six weeks to regain 60% of its strength. Because the injury involves both the disk and the facet joints, it is more difficult for the joint to stabilize itself and recurrence is frequent. The condition is progressive and may lead to spinal stenosis, instability and degenerative spondilolisthesis.
In this regard, it has been shown in laboratory that a compression injury is easily produced by compressing an intervertebral joint between 2Mpa to 6Mpa. It has also been shown that a torsional injury can be seen with as little as 2 to 3 degrees of forced rotation requiring only 22 to 33 Newton meter of torque.
In practice, it has been shown that 64% of the patients complaining of backache and sciatica, or of sciatica alone, exhibit torsional injuries whereas 35% of said patients exhibit axial compression injury. The torsional injury occurs mainly at the fourth level, that is between lumbar vertebral L4 and L5. It has also been shown that almost 100% of the fourth joints problems are torsional injuries. On the other hand, almost 100% of the compression injuries occur at the L5/S1 level, that is between the 5th lumbar vertebra L5 and the 1st sacral vertebra S1. Double injuries, that is joint injured with both compression and torsion, occurs in 20% of the cases, most invariably at the L5/S1 level.
The probalities of injuries by either compression or torsion are given hereinafter in table 1. As can be seen, the importance of frequency of torsional injury cannot be overlooked. As can also be seen, the probability of a third type of injury giving symptoms is very remote. As a matter of fact, a third part of injury as so far not be recognized in autopsy material.
TABLE 1 ______________________________________ CLINICAL DETERMINATION OF THE VARIOUS PROBABILITIES OF INJURIES JOINT P (injury) P (compression) P (torsion) ______________________________________ L5/S1 47% 98% 22% L4/L5 47% 1%&lt; 76% L3/L4 5%&lt; 1%&lt; 1%&lt; L2/L3 1%&lt; 1%&lt; 1%&lt; L1/L2 1%&lt; 1%&lt; 1%&lt; 100% 100% 100% ______________________________________
It should be noted from the above description of pathology that both types of injuries can give rise to identical symptomoloty that is back pain, back pain and sciatica or sciatica alone. As a result, symptoms cannot be used to diagnose a type of injury because identical symptoms may arise from different injuries.
It is also well known in the art that low back pain is the leading cause of disability in North America today, affecting from 8 to 9 million people. It is the most common disability in persons under the age of 45 and the third after arthritis and heart decease in those over 45. It is also estimated that 2 of 3 persons would have lumbar pain at sometimes of their life, usually between the ages of 20 to 50. The fact that problems are so common in people of working age is not coincidental. Indeed, most back problems are work-related.
As the injury caused by a certain task cannot be identified from the patient's symptoms, it is not possible to relate directly a given task to an injury mode, although such a relationship is central to the definition of a task that will not injure a specific worker.
The economic effects of back pain and injury are staggering. Back problems are second only to the common cold as a cause of absenteeism in the industry. It is moreover responsible for 93 million lost workdays every year and is a leading cause of reduced work capacity.
Hence, the incentive for prevention of back injury is very large.